1. Field of the Invention
The present invention relates to an inkjet printer in which a filter is arranged in an ink flow passage, and in more detail, to an inkjet printer which can efficiently execute storage and discharge of air bubbles flowing in an ink flow passage in which a filter is arranged.
2. Description of the Related Art
An inkjet printer (hereinafter, called “printer” simply) is provided with a filter disposed in an ink flow passage for removing foreign objects and air bubbles in the ink flow passage in such a manner as to accurately eject liquids (ink) from inkjet nozzles. The air bubbles removed by the filter are stored in the ink flow passage, pass through the filter in a recovery operation for each constant interval, and are discharged from the inkjet nozzles.
The filter removes the foreign object or the air bubbles to create excellent printing, and on the other hand, attachment of the air bubbles to the filter increases pressure losses of the filter depending on ink properties or an ink flow amount and raises a problem of causing a print failure.
At the time of discharging the air bubbles removed with the filter in the recovery operation, since the ink is also discharged simultaneously, it is necessary to restrict an ink amount to be discharged by extending the recovery interval (that is, reducing the number of times of the recovery operations), for example.
The following measures are proposed for solving these problems.
The first measure is to dispose an evacuation space in the upward direction of gravity (upward in the perpendicular direction) upstream of the filter. In consequence, it is possible to remove the air bubbles flowing together with the ink by the filter and to let out the air bubbles into the evacuation space.
The second measure is to reduce pressures in a filter portion at recovery operation for pressing a deformable member of the filter portion against the filter. Inconsequence, there is proposed an inkjet printer which increases a discharge efficiency of the air bubble, extends the recovery interval, and restricts an ink amount to be discharged.
Japanese Patent Laid-Open No. 2006-168224 discloses the construction corresponding to the first measure as described above, in which the ink is separated from the air bubble by the filter and the air bubble is let out to the evacuation space. However, an ink introducing port and an ink feeding port are arranged substantially on a straight line and there is almost no ink stream for guiding the air bubble to the evacuation space. Therefore, in a case where the ink stream is sequential, the air bubble is attached to the filter depending on ink properties or a size of the air bubble and an ink flow amount, which reduces an effective area of the filter. Thereby the pressure loss is increased, thus creating a possibility of causing a printing failure. In addition, since the evacuation space is right above the filter, when the ink flow amount is increased, the pressure in the filter portion is decreased and the separated air bubble is expanded, there is a possibility that the air bubble is again involved in the ink stream.
Japanese Patent Laid-Open No. 2006-051832 discloses the construction corresponding to the second measure as described above, in which the deformable member is pressed against the filter for improving the discharge efficiency of the air bubble. According to this construction, the deformable member requires flexibility, and further, since the flexibility is difficult to be compatible with a percolation performance of water vapors or gases of the deformable member itself, there is a possibility that the air bubbles grow due to gas percolation from the deformable member to inhibit extension of the recovery interval.